Prior to the present invention, as shown by Wirth et al U.S. Pat. No. 3,838,097, assigned to the same assignee as the present invention, polyetherimides were prepared by effecting reaction between an alkali metal bisphenoxide and a bis(nitrophthalimide) in the presence of a dipolar aprotic solvent. Valuable results were achieved by the practice of the aforementioned method of Wirth et al resulting in the production of a variety of useful polyetherimides which could be employed in different applications. The present invention is based on the discovery that unlike the method of Wirth et al, based on the intercondensation of difunctional reactants, polyetherimides also can be made by the self-condensation of a hydroxyaryl phthalimide salt having a nuclear bound leaving radical on the phthalimide ring. The polyetherimides of the present invention have been found to be useful high performance thermoplastics.
The polyetherimides of the present invention comprise chemically combined units of the formula, ##STR1## where R is a trivalent C.sub.(6-13) aromatic organic radical, R.sup.1 is a divalent C.sub.(6-30) aromatic organic radical and X is selected from --O--, or --S--.
Radicals included within R of formula (1), are for example, ##STR2## Radicals included within R.sup.1 of formula (1), are for example, ##STR3## where Q is a member selected from the class consisting of --O--, ##STR4## and C.sub.x H.sub.2x, where x is an integer equal to 1 to 5 inclusive.
There is also provided by the present invention, a method for making polyetherimide which comprises,
(A) heating a mixture comprising a phthalimide salt of the formula, ##STR5## and a dipolar aprotic solvent,
(B) allowing the mixture to cool to ambient temperatures and
(C) effecting the precipitation of polyetherimide from the mixture of (B), where Y is a nuclear bound leaving group selected from the class consisting of chloro, fluoro and nitro, M is an alkali metal ion or ammonium salt and R and R.sup.1 are as previously defined.
The phthalimide salts of formula (2) can be made by heating a mixture of a nonpolar solvent and an alkoxide base or amine and a hydroxy aryl phthalimide of the formula, ##STR6## where R, R.sup.1, X, and Y are as previously defined.
There are included within the hydroxyaryl phthalimides of formula (3) compounds such as ##STR7##
The polyetherimides of the present invention can be employed to make films, coatings, etc., can be used as an injection moldable plastic to produce a variety of tough molded parts, etc. The polyetherimides consisting essentially of chemically combined units of formula (1) can be reinforced with various particulated fillers such as glass fibers, silica fillers, carbon whiskers, to up to 50% by weight of the resulting total blend. Reinforcement of the polymer can be accomplished prior to polymer formulation by effecting polymerization in the presence of filler, melt blending and solution blending also can be used.
In the practice of the invention the phthalimide salt of formula (2) can be self-condensed in a dipolar aprotic solvent such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, etc. The phthalimide salt can be made by effecting reaction between substantially equal molar amounts of a hydroxyaryl phthalimide of formula (3) and an alkali metal alkoxide, such as anhydrous sodium methoxide, potassium t-butoxide, or amines as triethylamine, etc. In order to facilitate salt formation there can be used a nonpolar solvent to minimize the attack of the phthalimide ring with the alkoxide ion. Suitable nonpolar solvents which can be used to facilitate the production of the phthalimide salt are, for example, benzene, toluene, hexane, etc. After salt formation which can be achieved by heating nonpolar solvent alkali alkoxide and hydroxy aryl phthalimide of formula (3) mixture at a temperature in the range of from 25.degree. C. to 125.degree. C. Prior to the addition of the dipolar aprotic solvent, the nonpolar solvent can be stripped from the mixture if desired, or it can be left in the mixture during the self-condensation reaction.
The self condensation of the phthalimide salt of formula (2) can be effected in the presence of a dipolar aprotic solvent as previously defined. After the polymerization the resulting polyetherimide can be recovered from the polymerization mixture by the use of a precipitating solvent such as methanol, hexane, water, etc. The polymerization mixture, for example, can be allowed to cool to ambient temperatures and thereafter poured into excess methanol. The resulting precipitated product can then be filtered or recovered by other conventional means such as centrifuging, etc.
The hydroxyarylphthalimides of formula (3) can be made by effecting reaction between substantially equal molar amounts of a substituted phthalic anhydride of the formula, ##STR8## and a hydroxyaryl amine of the formula, EQU NH.sub.2 R.sup.1 XH, (5)
where R, R.sup.1, Y and X are as previously defined. Reaction can be facilitated in the presence of an organic solvent, such as acetic acid.